Stored procedure failing on nightly cycle

[jer006]

Hi,
This is more of a general question...

I have a series of stored procedures (chain of procedures) in db2 on
an AS400 which are executed from a SQL Server Job, when I execute the
job manually during the day (or when I execute the stored procedures
in db2 on the AS400 directly) everything completes successfully.
However when the procedures are executed on its scheduled cycle at
3am
in the morning it fails most every morning with a generic *N error.
This has been happening for a month now and IBM support have had us
put on a trace of activity on the AS400 which yielded a 100,000 page
report for 10 minutes of timeframe - the solution they had me do was
to drop and recreate the procedure which solved nothing
unfortunately!

I built my own logging into the procedures which captures when they
start and finish and was able to trace the failure in the sequence
down to a select statement in one of the procedures however this does
not explain why it fails sometimes during the nightly cycle and not
other times with a generic uninformative error!

I am not an AS400 or DB2 expert but can anyone tell me the sort of
things that I should be looking for on the AS400 or what sort of
traces (sql trace, error logs, process activity etc) I can run on the
AS400 directly to hopefully track down this problem...

I can run this procedure all day long and it succeeds without any
issues the failure only happens on the nightly cycle which leads me
to
think there is a conflict or something is clashing with it...

Any help would be much appreciated as I really want to get to the
bottom of this!

Thanks
Jeremy.